Against the Wall High: Blood Pressure

Blood is under pressure as it is pumped around the body, and this pressure exerts on the arterial wall. The health status of this pressure is dependent on the force of the pumping, the quantity of blood pumped and the condition of the arteries. While blood pressure can change by the minute or second its influenced by temperature, diet, mood, activity, medication and other factorsconsistently high blood pressure that rarely abates is dangerous to health. Called hypertension, high blood pressure is even more dangerous because it often develops silently, giving no outward symptoms of its escalation.  Thus, the best way to know blood pressure is via testing. However, due to the influence of many factors (including white coat syndrome, where the patient get nervous at the doctors office), it takes multiple and consistent high test readings to confidently diagnose hypertension. 

When talking blood pressure measurement, two main forces must be considered. Systolic pressure is usually the higher of the two numbers in a test reading and measures the force when the heart contracts to pump blood. Diastolic is the lower number and measures the force during the hearts relaxation between pumps. A reading below 120 mmHg (systolic) over 80 mmHg (diastolic) is a median of sorts, as readings below this figure is considered healthy for adults. A reading where the systolic result is higher than 120 but below 139 and the diastolic is above 80 but below 89 is considered pre-hypertensive, while readings above 140/90 is considered hypertensive.

Elevated blood pressure can be physically due to a greater pumping force from the heart or from, more commonly, narrowing of the arteries, such as in cardiovascular disease (CVD). High blood pressure can further damage the arteries and make the heart work harder, increasing the risk of heart and cardiovascular problems, including stroke. Further, if blood vessels to the kidneys are affected, kidney failure risk can go way up.

The kidneys are actually the key organ in the role of salt in blood pressure. The kidneys control salt levels, usually passing excess salt to the urine. When salt level is higher than the kidneys can handle, the salt ends up in the blood, which then draws more water; this increases blood volume, which is one way to increase blood pressure. Now couple this scenario with existing arterial narrowing due to CVD, and you get a double-whammy of hypertension dangers. Thus, kidney health is an important part of the blood pressure management equation.

The influence of salt, especially from processed foods and staples such as cheese, soup and bacon, has historically focused attention on the diet. Studies by the National Institutes of Health (NIH) resulted in the creation of the DASH (Dietary Approaches to Stop Hypertension) diet, which is promoted by the NIHs National Heart, Lung and Blood Institute and the American Heart Association (AHA). In the first trial, reported in 1997, 459 adults with blood pressure under 160/95 consumed a typical American diet low in fruits, vegetables and dairy, but high in fat for three weeks.¹ They were then randomly assigned to either a control diet, a diet rich in fruits and vegetables or a combination diet rich in fruits, vegetables and low-fat dairy, but low in saturated and total fat, for eight weeks. The combination diet helped lower blood pressure better than did the control diet; the results were more pronounced in the subgroup of hypertensive subjects. This research gave birth to the DASH diet focused on fruits, vegetables, fish, poultry and whole grains instead of salt, high-fat dairy and red meat.

Then in 2001, results from a second trial showed salt reduction along with adherence to the DASH diet work together to lower blood pressure more than either approach alone.² The trial featured 419 subjectssome hypertensive, some notwho were assigned to either a typical American diet or the DASH diet, and ate foods with high, intermediate or low sodium content for 30 consecutive days, in a random order. Blood pressure decreased along with the lowering of salt content, in both hypertensive and non-hypertensive subjects, and across race and gender. The DASH diet also lowered blood pressure across the range of variables, but the effect was more pronounced at higher sodium intake; the best benefit to blood pressure was when DASH diet was combined with the lowest salt intake.

Given the focus of the DASH diet, it should be no surprise the oft-heralded Mediterranean diet, which also favors plant foods and healthy fat and protein foods, has also been shown beneficial to blood pressure control.³ In the 2009 study of a cohort of 8,594 participants aged 20 to 95, researchers found an inverse link between fruit/vegetable intake and risk of hypertension among those with low olive oil consumption (less than 15 g/d). However, a 2011 research report in the journal Hypertension detailed how Greek children have elevated sodium intake from hidden sources (not table salt or cooking salt), mainly processed versions of foods that are daily staples of the Mediterranean diet, such as cheese and bread.⁴

This dietary research raises the question: Are the plant foods in the DASH and Mediterranean diets beneficial due to substitution or do they have protective effects? If recent research on botanical-based products is any indication, plants have protective or therapeutic benefits to blood pressure management.

First, a diet rich in fresh fruits and vegetables is thus high in vitamin and mineral intake. Increased intake of calcium, magnesium and potassium has been inversely linked to blood pressure levels, with one study showing salt reduction, particularly in combination with increased intake of these minerals, substantially lowered blood pressure.⁵

On its own, magnesium intake may be inversely connected to incidence of hypertension, while deficiency has demonstrated a negative effect on arterial thickness and stiffness, arterial pressure and incidence of hypertension.^6,7 The mineral has also shown the potential to regulate blood pressure,⁸ possibly by modulating vascular tone and influencing vasodilation and inflammation.⁹ Who benefits from magnesiums blood pressure benefits is not entirely clear, as Korean researchers found oral magnesium supplementation in healthy adults (diabetes-free, normatensive and with normal magnesium levels) had no effect, while those with hypertension and normal magnesium levels experienced lower blood pressure after supplementation.¹⁰

Magnesium is needed for optimal absorption of calcium, another mineral that has shown some potential to positively affect blood pressure. A study of more than 900 middle-aged men found consumption of dairy products and dietary calcium were both significantly and independently associated with low levels of systolic blood pressure.¹¹ As shown in the research on DASH, the key to dairys positive role in blood pressure is in being low-fat; A Harvard trial confirmed this theory, as a cohort of 28,886 U.S. women showed intakes of low-fat dairy products, calcium and vitamin D were each inversely associated with hypertension.¹² Looking further at calciums role in cardiovascular health, a 2010 New Zealand study found two years of calcium supplementation (600 mg/d or 1200 mg/d) in 323 generally healthy men had no significant effect on ratio of high-density lipoprotein (HDL) to low-density lipoprotein (LDL) cholesterol, weight, fat mass, lean mass, triglycerides or total, LDL, or HDL cholesterol, but there were downward trends in blood pressure in the treatment group.¹³ Specifically, those with low calcium intake who received 1,200 mg/d  calcium had an average drop of 4.2 mm Hg systolic and 3.3 mm Hg diastolic pressure, compared to those taking placebo. Similar results were found for those with low magnesium intake.

Calcium absorption requires sufficient vitamin D, another essential nutrient with some ties to blood pressure. An inverse relationship between plasma 25-hydroxyvitamin D levels and risk of incident hypertension in young women was reported in a late 2008 study from Harvard Medical School researchers, who noted young women with low levels of vitamin D had a substantially higher risk of hypertension than women with sufficient levels of the vitamin.¹⁴ In 2011, a report from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, concluded while clinical evidence is lacking, observational data suggests vitamin D supplementation could potentially have a strong preventive effect on some of these conditions and could reduce race-related disparities in their prevalence.¹⁵

Two other essential vitamins are possibly involved in blood pressure. Vitamin C, which contributes to collagen production and vascular flexibility, may affect blood pressure by targeting increased oxidative stress associated with the condition.¹⁶ Japanese researchers found 600 mg/d ascorbic acid significantly reduced systolic and pulse pressure in elderly patients being treated for hypertension.¹⁷ And 1,000 mg/d of vitamin C added to antihypertensive therapy reduced systolic blood pressure and decreased oxidative stress in an Indian trial.¹⁸

Vitamin C taken along with vitamin E affects blood pressure and several related parameters. A University of Pisa, Italy, trial showed hypertensive men taking vitamin C (1 g/d) and vitamin E (400 IU/d) for eight weeks experienced significantly improved flow-mediated dilation (FMD) and arterial flexibility, as well as vasodilation and oxidative stress parameters.¹⁹ Similar research found hypertensive men taking vitamins C and E for eight weeks had significantly lower systolic and diastolic blood pressure, in addition to higher serum antioxidant capacity.²⁰

A closer look at vitamin E reveals the effects of specific fractions on blood pressure. Early work from a Malaysian research team found as much as 320 mg/d of tocotrienol-rich vitamin E (TRE) was well-tolerated and increased plasma concentrations of alpha-, delta- and gamma-tocotrienol, but did not significantly affect arterial compliance, plasma total antioxidant status or LDL cholesterol levels in normal subjects.²¹ However, their subsequent research revealed a self-emulsifying TRE preparation in varying dosages (50 mg/d, 100 mg/d and 200 mg/d for two months) generated a trend toward arterial compliance.²² Further, results from  Texas Southern University, Houston,  research team indicated supplementation with gamma-tocotrienol may enhance total antioxidant status, reduce lipid peroxidation in plasma and blood vessels and inhibit blood pressure increases.²³ Their follow-up work detailed how gamma-tocotrienol may improve blood pressure by increasing nitric oxide synthase (NOS) activity, which is reduced in hypertension.²⁴

NOS is an enzyme that  aids in the production of nitric oxide (NO) from L-arginine, an amino acid that can reduce arterial blood pressure benefit both inter-media thickness and overall endothelial function.^25,26 Arginine is normally produced in the body, but is also available from several plant and animal sources of protein, such as dairy and seafood.

In 2009, Japanese researchers reported on their population-based, cross-sectional study of 7,585 subjects (3,499 men and 4,086 women, aged 40 to 69 years) and associations between dietary intakes of total, animal, and plant protein and blood pressure.²⁷ After adjusting for age, sex, community, body mass index, antihypertensive medication use, ethanol intake, smoking, and dietary intakes of sodium, potassium and calcium, they found a 25.5-g/d increment in total protein intake was associated with a decrease in systolic blood pressure of 1.14 mmHg and in diastolic blood pressure of 0.65 mmHg; a 19.9-g/d increment in animal protein intake was associated with a decrease in systolic blood pressure of 1.09 mmHg and in diastolic blood pressure of 0.41 mmHg.

Peptides in milk and whey may be important to the blood pressure effects of these foods, as research has suggested such peptides may inhibit vasoconstrictor enzymes such as angiotensin-1-convering enzyme (ACE), and positively impact vasodilation.²⁸ Tetrapeptides (alpha-lactorphin and beta-lactoglobulin) from milk protein administered to spontaneously hypertensive rats improved vascular relaxation, influencing both endothelial function and endothelium-independent relaxation.²⁹

The milk peptides isoleucine-proline-proline (IPP) and valine-proline-proline (VPP) inhibit angiotensin converting enzyme (ACE), which plays a role in the creation of vasoconstrictors that narrow vessels. Research has demonstrated long-term intake of these two ACE-inhibiting peptides slows the development of hypertension.³⁰ A 2008 meta-analysis confirmed food protein peptides significantly lower both systolic and diastolic pressure, and the majority of studies reviewed featured IPP and VPP.³¹ A 2010 Nutrition Journal publication detailed a randomized, placebo-controlled, double blind, crossover study involving 70 subjects with pre-hypertension or stage 1 hypertension were given either two capsules of milk protein hydrosylate (MPH1, each capsules containing 7.5 mg IPP), MPH2 (each containing 6.6 mg methionine-alanine-proline, 2.3 mg leucine-proline-proline and 1.8 mg IPP) or placebo (containing cellulose) for four weeks.³² The only significant effect found in the trial was a decrease in systolic blood pressure of 3.8 mmHg and in diastolic BP by 2.3 mmHg in stage 1 hypertensive patients who took MPH1, compared to placebo.

Similar results were also found in University of Minnesota, Minneapolis, human research on whey-derived peptide supplementation;³³ researchers found six weeks of supplementation led to significant reductions in systolic and diastolic blood pressure, in addition to improvements in LDL cholesterol and inflammatory markers.

Soy protein intake has also been inversely linked to both systolic and diastolic pressure, with the association growing stronger with age.³⁴ Researchers from Beth Israel Deaconess Medical Center, Boston, provided additional evidence, noting substituting soy nut for non-soy protein could significantly reduce blood pressure in both normotensive and hypertensive women, possibly via improved endothelial function and reduced inflammation.³⁵  Similarly, the addition of 10 g/kg/d of soy powder (31 percent isoflavones) to a high-fat diet can decrease oxidative damage, inhibit increases in blood pressure and influence NO production for endothelial benefit.³⁶

Fermented soy, called natto, and its peptides have also exhibited ACE-inhibiting properties and overall antihypertensive effects.³⁷ Natto may abate intimal thickening in the arteries and, due its nattokinase enzyme content, may also address blood pressure by breaking down fibrin, a protein involved in clotting.^38,39  In a 2008 study, untreated hypertensive adults (systolic=130-159 mmHg) taking nattokinase (2,000 fibrin-degrading units/capsule) for eight weeks had significant reduction in systolic (-5.5 mmHg) and diastolic (-2.8 mmHg) blood pressure.⁴⁰

The DASH and Mediterranean diets both call for lean and sea protein, and science is showing fish consumption has vascular protective effects and exerts a positive effect on diastolic blood pressure.^41,42 In support of this dietary influence, an Italian study concluded hypertensive adults who made a long-term dietary change to consume more fish and vegetables experienced improved blood pressure management.⁴³ Epidemiological data indicated an inverse relationship between total omega-3 intake from food and diastolic and systolic blood pressures, with the greatest impact from long-chain omega-3 intake from fish.⁴⁴ And in a 2007 research review, consumption of fish oil and its omega-3 EFAs was credited with a small but significant benefit to blood pressure, particularly among adults with hypertension.⁴⁵

Plants are a huge part of the anti-hypertensive diet. Besides providing a range of vitamins, minerals and other nutrients, fruits and other plants offer a number of compounds that contribute to blood pressure control.

Grapes and wine are rich in polyphenols and have shown promise in addressing blood pressure concerns. Wine can improve endothelial function and decrease blood pressure by reducing oxidative stress, in addition to inhibiting expression of pro-inflammatory factors that are involved in angiotensin II-induced hypertension and endothelial dysfunction.^46,47  Animal research has found wine polyphenols decrease blood pressure by improving endothelium-dependent dilation and antioxidant status.⁴⁸

Grape seed extract (GSE) made from unfermented red and white wine grape seeds (as MegaNatural BP®, from Polyphenolics) displayed various blood pressure benefits in a series of studies conducted at the University of California, Davis. A randomized trial involving subjects with pre-hypertension who were given either 300 mg/d GSE or placebo for two months found both systolic and diastolic pressure were lower in the treatment group, with no changes to serum lipids or glucose values.⁴⁹ It was also discovered GSE helps relax the endothelium via activation of an enzyme pathway that involves endothelial NOS.⁵⁰ Further, the researchers randomized subjects with metabolic syndrome to receive either 150 mg/d or 300 mg/d GSE for one month and recorded blood pressure at both baseline and the end of the supplementation period.⁵¹ They found reduction of both systolic and diastolic blood pressure in the GSE group, without changes to serum glucose or lipids.

Chinese researchers also found administration of GSE reduced systolic blood pressure, most likely due to the presence of proanthocyanidin flavonoids in the extract.⁵² Pine bark has proven a rich source of oligomeric proanthocyanidins (OPCs) and a potent attenuator of blood pressure. Joint German-United States university research showed 200 mg/d French maritime pine bark extract (as Pycnogenol®, from Horphag, supplied by Natural Health Science) significantly decreased systolic blood pressure, compared to placebo, although the results on diastolic pressure failed to reach significance.⁵³ Then in a 2008 study, 100 mg/d of Pycnogenol improved endothelial function, decreased endothelin-1 concentrations and increased NO levels in plasma in patients with hypertension.⁵⁴ Similarly, 480 mg/d of New Zealand pine bark extract  (as Enzogenol®, from ENZO Nutraceuticals, supplied by B&D Nutritional Ingredients), along with vitamin C (240 mg/d),  taken for 12 weeks significantly reduced systolic blood pressure.⁵⁵

Proanthocyanidins are made from fellow phenol catechins; tea contains both kinds of flavonoidsincluding epigallocatechin-3-gallate (EGCG)and has generated positive effects on both endothelial function and hypertension in published research.⁵⁶ In animal study, green tea limited hypertension by addressing oxidative damage.⁵⁷  Human research confirmed blood pressure reduction from administration of green tea.⁵⁸ University of Florida, Gainesville, scientists gave healthy adults (aged 21 to 70) either a capsule of standardized green tea (Camilla sinesis) or placebo twice daily and tested for various cardiovascular parameters. After three weeks, systolic and diastolic pressures were decreased by 5 mmHg and 4 mmHG, respectively, with systolic pressure remaining low after three months.

Anthocyanins from fruit and plant consumption are another flavonoid compound with a possible beneficial role in blood pressure . Anthocyanins (water-soluble pigments) from purple corn, purple sweet potato and red radish administered to hypertensive rats decreased blood pressure and heart rate in a Japanese trial,⁵⁹ while chokeberry anthocyanins given to adults for two months significantly lowered both systolic and diastolic blood pressure in a Polish study.⁶⁰

Pomegranates are rich in anthocyanins, tannins (including catechins) and other polyphenolic compounds. Pomegranate juice (50 mL) given to hypertensive patients for just two weeks significantly reduced systolic blood pressure and ACE activity in an Israeli trial.⁶¹ The same research team looked at long-term intervention, finding pomegranate juice consumption by hypertensive adults over a three-year period reduced systolic blood pressure by 21 percent after just one year.⁶² Pomegranate consumption did appear to improve vascular health by decreasing carotid intima-media thickness.

Other plants and other plant compounds have also provided blood pressure-lowering evidence. In 2002, Egyptian researchers reported olive leaf extract EFLA® 943 (as Benolea®, by Frutarom) showed hypotensive effects in hypertensive rats, noting the extract reversed adverse vascular changes.⁶³ Then in  a 2003 South African animal trial resulting in the inhibition of severe hypertension and atherosclerosis after six weeks of olive leaf administration, scientists credited triterpenoids from Greek and African olive leaf with the benefits.⁶⁴ In 2008, German and Swiss researchers studying olive leaf extract in twins, in order to negate genetic differences, found 500 mg/d resulted in a significant decline in systolic pressure vs. an increase in pressure in the placebo group, while those taking 1,000 mg/d olive leaf extract had a significant reduction in systolic pressure, compared to placebo.⁶⁵  Most recently, a 2011 research report from University of Indonesia, Jakarta, detailed how 500 mg/d EFLA 943 twice daily for eight weeks was comparable to captopril (an ACE-inhibiting drug used for treating hypertension and congestive heart failure) in lowering systolic and diastolic pressure in stage 1 hypertensive patients.⁶⁶

The leaves of Ginkgo biloba, a potent vasodilator via the NO pathway, have been studied for benefits to hypertension management. A 2006 Japanese study confirmed ginkgo extract restored vasodilatory function and significantly improved systolic pressure in hypertensive animals.⁶⁷ Additional Japanese research showed a standardized ginkgo extract (as EGb 761) can suppress age-related increases in blood pressure and exhibit strong anti-thrombotic and antioxidant effects in stroke-prone hypertensive animals.⁶⁸ Subsequent investigation of long-term ginkgo administration in aging animals revealed no effect on blood pressure, but impaired peripheral circulation and increased liver weight, suggesting ginkgo use in elderly population may need to be assessed for  heart rate and liver effects.⁶⁹

Garlic also has vasodilatory properties, credited often to its allicin constituent, and has generated a range of researched benefits to both systolic and diastolic blood pressure, although the population most benefited from garlic is not clear. A 2008 Australian meta-analysis collected evidence that suggested various garlic preparations are superior to placebo in reducing blood pressure in hypertensive subjects,⁷⁰ while a Hartford Hospital, CT, meta-analysis concluded garlic reduced blood pressure in subjects with elevated systolic pressure, but not those with normal systolic readings.⁷¹

Clinically, a 2004 Indian trial on short-term garlic supplementation in essential hypertensive patients resulted in a significant decline in both systolic and diastolic pressure, as well as a modest increase in total antioxidant status and a subsequent reduction in oxidized LDL cholesterol.⁷²

Many different mechanisms have been suggested, as research has pointed to garlics antioxidant properties and allicin content as keys to the botanicals blood pressure-lowering benefits.^73,74,75 Further, bioavailability may be a deciding factor, as time-released garlic powder tablets were shown to be more effective for the treatment of mild and moderate arterial hypertension than are regular garlic supplements in Russian research.⁷⁶

Studies on aged garlic extract (AGE) support the assertion benefits to blood pressure depend on the form of garlic used. In an animal trial, AGE and powdered garlic reversed increasing blood pressure in after 10 weeks of invtervention.⁷⁷ In human research, hypercholesterolemic men taking 7.2 g/d of AGE supplementation for six months experienced a 5.5-percent decrease in systolic blood pressure and a modest reduction in diastolic blood pressure in one study,⁷⁸ while intervention with AGE plus vitamin B1 and ginseng extract effectively lowered blood pressure in hypertensive, but not normo-tensive patients, in another study.⁷⁹

In food, at least, garlic goes hand-in-hand with tomatoes, and both are central to the diets pinpointed as anti-hypertension. In fact, researchers using USDA food composition databases to analyze the phytochemical content of the DASH diet discovered a higher lycopene (the primary tomato carotenoid) and flavonoid content in DASH than in an average American diet.⁸⁰ In other research, lycopene-rich tomato extract (250 mg/d, as Lyc-O-Mato®, from Lycored) significantly decreased both systolic and diastolic blood pressure in grade-1 hypertensive patients after eight weeks of supplementation, compared to placebo.⁸¹ 

From food to supplements, natural products and their wealth of nutrients and other constituents have shown great promise in addressing endothelial health and blood pressure management, as evidence in numerous animal and human in vivo research trials.

References are on the next page...

References for "Against the Wall: Blood Pressure"  

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